1. Field of the Invention
The present invention relates to an apparatus and method for measuring a liquid level using acoustic waves.
2. Description of the Related Art
Referring to FIG. 1, a conventional liquid level gauge includes a vessel 100 containing a predetermined amount of liquid 105. An optical sensor is included, comprised of a light-emitting portion 110 for emitting light, and a light-receiving portion 113 that receives the light emitted from the light emitting portion 110, and determines an amount of transmission, both of which are disposed at sidewalls of the vessel 100. The amount of transmission received by light receiving portion 113 indicates the quantity of the liquid 105 in vessel 100. Liquid 105 is supplied to and withdrawn from the vessel 100 by inlet 115 and outlet 118, respectively.
The optical sensor described above measures the level of liquid 105 by detecting an amount of light either reflected from the vessel 100, or transmitted into the liquid 105, after being radiated from the light emitting portion 110. However, this approach may require additional optical sensors for accurate liquid level measurement, since a liquid level can be measured only when the liquid 105 is filled up at least to the level at which the light emitting portion 110 and the light receiving portion 113 are mounted. For example, as shown in FIG. 1, if the height of the liquid 105 is L, which is less than that the height of the light emitting portion 110 and the light receiving portion 113, a liquid level measurement cannot be made. Thus, this approach restricts the liquid level measurement range, and would require additional cost if the measurement range were to be increased due to the need to add additional optical sensors. Furthermore, this approach is limited in its applications since the liquid must be sufficiently transparent for light to be transmitted.
If the conventional liquid level gauge is used in a printer, an error may occur in measuring the storage level of the liquid 105 since solidified ink may remain on an inner wall of the vessel 100 when the ink fills the vessel 100 and flows into the inlet 115 or out of the outlet 118.
To solve the above problems, it is an objective of the present invention to provide an apparatus and method for measuring a liquid level using acoustic waves that can precisely measure a liquid level without restrictions on the type of liquid, e.g., whether the liquid is transparent or opaque.
Accordingly, the present invention provides an apparatus for measuring a liquid level including: a vessel containing a liquid; a plurality of acoustic tubes having first ends disposed vertically along a sidewall of the vessel for each of liquid levels to be measured and connected to the inside of the vessel, and second ends connected to a common tube; and a storage level sensor board that generates an acoustic wave in the vessel, receives an acoustic wave propagated through one or more of the acoustic tubes and the common tube, and determines the level of liquid in the vessel based on the received acoustic wave.
Preferably, the storage level sensor board includes: an acoustic generator that generates an acoustic wave of predetermined frequency; a speaker that transmits the acoustic wave generated by the acoustic generator into the vessel; an acoustic sensor that detects the acoustic wave propagated through one or more of the plurality of acoustic tubes; an analog-to-digital converter that digitalizes a signal output from the acoustic sensor; and a data processor that evaluates a liquid level from data output from the analog-to-digital converter. Preferably, the storage level sensor board further includes a barrier wall disposed adjacent to the plurality of acoustic tubes, and supported at an upper surface of the vessel so that the barrier wall may be separated from the bottom of the vessel by a predetermined distance. Furthermore, it is preferable that the speaker is disposed between the barrier wall and the sidewall of the vessel at which the plurality of acoustic tubes are disposed.
The present invention also provides a method of measuring a liquid level including the steps of: generating an acoustic wave in a vessel containing a liquid; arranging a plurality of acoustic tubes disposed vertically along a sidewall of the vessel, and receiving an acoustic wave propagated through one or more acoustic tubes which are not submerged in the liquid; and outputting the received acoustic wave as an electrical signal, comparing the output electrical signal with tabulated data and evaluating a liquid level.